Best way to extend the MapChart visualization

I have implemented a factory like the following:

internal sealed class AttributeMapFactory : ConfiguredVisualFactory<MapChart> {
    internal AttributeMapFactory() : base(
        VisualTypeIdentifiers.MapChart2, // Type identifier for base visualization  
                                         // New Type identifier  
        VisualCategory.Visualization,    // Visual category  
        Properties.Resources.layers,     // Icon  
    ) // License  

Now I would like to extend my visual by adding som C# Forms controls to it (Labels and ToggleButtons). What is the best way to implement this? The MapChart class is sealed and therefore cannot be extended. Is it possible to make a CustomVisualization that consists of standard Forms controls in addition to a Panel containing a MapChart or is there an alternative way of implementing it?